NR2B-Selective N-Methyl-D-aspartate Antagonists: Synthesis and Evaluation of 5-Substituted Benzimidazoles

Article abstract of DOI:10.1021/jm030483s

Two classes of 5-substituted benzimidazoles were identified as potent antagonists of the NR2B subtype of the N-methyl-D-aspartate (NMDA) receptor. Selected compounds show very good selectivity versus the NR2A, NR2C, and NR2D subtypes of the NMDA receptor as well as versus hERG-channel activity and α₁-adrenergic binding. Benzimidazole 37a shows excellent activity in the carrageenan-induced mechanical hyperalgesia assay in rats as well as good pharmacokinetic behavior in dogs.

Full text of DOI:10.1021/jm030483s

J . Med. Chem. 2004, 47, 2089-2096
2089
NR2B-Selective N-Meth yl-D-a sp a r ta te An ta gon ists: Syn th esis a n d Eva lu a tion of
5-Su bstitu ted Ben zim id a zoles
J ohn A. McCauley,*,† Cory R. Theberge,† J oseph J . Romano,† Susan B. Billings,† Kenneth D. Anderson,†
David A. Claremon,† Roger M. Freidinger,† Rodney A. Bednar,‡ Scott D. Mosser,‡ Stanley L. Gaul,‡
Thomas M. Connolly,‡ Cindra L. Condra,‡ Menghang Xia,‡ Michael E. Cunningham,‡ Bohumil Bednar,‡
Gary L. Stump,| J oseph J . Lynch,| Alison Macaulay,# Keith A. Wafford,# Kenneth S. Koblan,‡ and
Nigel J . Liverton†
Departments of Medicinal Chemistry, Molecular Pharmacology, and Pharmacology, Merck Research Laboratories,
West Point, Pennsylvania 19486
Received September 25, 2003
Two classes of 5-substituted benzimidazoles were identified as potent antagonists of the NR2B
subtype of the N-methyl-D-aspartate (NMDA) receptor. Selected compounds show very good
selectivity versus the NR2A, NR2C, and NR2D subtypes of the NMDA receptor as well as
versus hERG-channel activity and R1-adrenergic binding. Benzimidazole 37a shows excellent
activity in the carrageenan-induced mechanical hyperalgesia assay in rats as well as good
pharmacokinetic behavior in dogs.
In tr od u ction
The N-methyl-D-aspartate (NMDA) receptor is a gated
ion channel that is present throughout the mammalian
central nervous system (CNS) and is activated by the
excitatory amino acid, glutamate. This receptor plays a
fundamental role in a number of physiological processes
and may provide an avenue for the treatment of such
disease states as stroke, Parkinson’s disease, and neu-
ropathic pain.1 Agents that block the NMDA channel,
such as ketamine, have been shown to alleviate pain in
human clinical trials; however, the small therapeutic
window relative to side effects such as hallucinations,
dysphoria, and loss of coordination makes such com-
pounds unattractive for chronic pain therapy.2,3 The
NMDA receptor is a hetero-oligomeric ion channel made
F igu r e 1. Structures of NR2B selective NMDA receptor
up of a combination of NR1 subunits (a-f) and at least
one of the four NR2 subunits (A-D).4,5 While the NR2A
subunit is ubiquitously expressed in brain, the NR2B
subunit is largely confined to structures in the forebrain
including the cerebral cortex, hippocampus, and olfac-
tory bulb.6 The reduced level of NR2B subunits in the
cerebellum suggests that NR2B-selective agents may
show an enhanced therapeutic window vs locomotor side
effects,7 and this hypothesis has been borne out in
several animal studies with NR2B selective compounds
such as 1 (ifenprodil)8,9 and 2 (CP-101,606).10 Recently,
a variety of structurally diverse compounds, such as
aminoquinoline 3,11 sulfoxide 4 (CI-1041),12 and benz-
amidine 513,14 have also shown selectivity for NR2B.15,16
We report here a series of structurally novel benzimid-
azole NR2B-selective NMDA antagonists that demon-
strate excellent activity in the carrageenan-induced
antagonists.
F igu r e 2. NR2B active benzimidazoles.
mechanical hyperalgesia assay in rats as well as good
pharmacokinetic properties in dogs.
Screening of the Merck sample collection led to the
identification of a benzimidazole derivative 6a (Figure
2) with modest NR2B activity (Table 2). This lead shares
a benzylpiperidine substituent in common with a num-
ber of published NR2B-selective compounds (see Figure
1). Issues with compound 6a included comparable
binding at the hERG potassium channel (see Table 2)
and R-adrenergic receptors. On the basis of this lead, a
rapid analogue synthesis was carried out to prepare a
series of 2-substituted benzimidazoles from o-phenylene-
diamine and a variety of acids. Of the approximately
100 benzimidazoles prepared (not shown), biphenyl
ether 7a (Figure 2 and Scheme 1), derived from
* To whom correspondence should be addressed. Phone: 215-652-
4133. Fax: 215-652-3971. E-mail: john_mccauley@merck.com.
† Department of Medicinal Chemistry.
‡ Department of Molecular Pharmacology.
| Department of Pharmacology.
#
Department of Pharmacology, Merck Sharp & Dohme Research
Laboratories, The Neuroscience Research Centre, Terlings Park,
Eastwick Road, Harlow, Essex, CM20 2QR, UK.
10.1021/jm030483s CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/11/2004

2090 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 8
McCauley et al.
Sch em e 1a
ant olefins were reduced under hydrogenation condi-
tions with concomitant N-benzyl loss providing 4-benzyl-
piperidines 26-30. Alkylation with ethyl bromoacetate
and ester hydrolysis gave acids 31-36, which could be
converted to benzimidazoles 6a , 6b, and 6d -e employ-
ing the appropriate phenylenediamine (8, 10, 14, 16).
The 5-hydroxyl group of 6c was then unmasked by
heating 6b in a solution of 48% HBr in H2O. Phenyl-
substituted derivatives 37a -e were prepared in a
similar fashion from 4-methoxy-1,2-phenylenediamine
(10) and acids 32-36 followed by demethylation.
Resu lts a n d Discu ssion
Compounds shown in Table 1 were evaluated in an
NR2B-selective binding assay (NR2B binding) and a
cell-based assay measuring Ca2+ flux in cells expressing
the NR2B subunit (NR2B Ca2+ influx).22 Selected
compounds were screened for hERG-channel activity
using an MK-499 binding assay23 and for R-adrenergic
activity using a prazosin binding assay.24 Compounds
were also counterscreened using a Ca2+ influx assay in
cells expressing the NR2A subtype. All compounds
described showed IC50 values greater than 10 µM. The
potency of the initial phenoxyphenylbenzimidazole com-
pound (7a ) was improved by hydroxylation of the
4-position on the benzimidazole ring (7e); however, a
more significant 80-fold enhancement was observed
when the hydroxy group was installed at the 5-position
(7f). Even though absolute hERG activity was higher,
compound 7f shows a 30-fold increase in selectivity over
hERG. We further hypothesized, on the basis of the lack
of activity of methylated derivative 7c and similarity
to other NR2B ligands, that a hydrogen bond donor was
necessary for good NR2B binding. This led to the
synthesis of methanesulfonamide 17a , which had a Ki
for binding to the NR2B receptor of 0.68 nM. This
compound also had excellent potency in the cell-based
assay, >150-fold selectivity over hERG and very low
R-adrenergic activity.
As shown in entries 17a -e in Table 1, binding activity
generally decreased with increasing steric bulk of the
sulfonamide substituent. These changes seem to have
little effect on activity in the counterscreens. Methyla-
tion of the sulfonamide nitrogen led to substantial loss
of activity (19), providing further evidence for the need
of a hydrogen-bond-donating substituent.
As a result of the enhanced potency and selectivity
seen by introducing hydrogen-bond-donating substitu-
ents on the benzimidazole ring of compound 7a , we
proceeded to apply the same strategy to the initial
screening lead 6a . By installing the 5-hydroxy group (6c,
Table 2), as in the phenoxyphenyl series, we achieved
a 280-fold increase in NR2B potency as well as a 2-fold
reduction in hERG binding. As shown in Table 2, these
derivatives (6c-e) were selective, showed similar SAR
profiles to the phenoxyphenyl derivatives described
above, and also benefited from increased aqueous
solubility.
a
Reagents and conditions: (a) EDC, HOBt, (4-phenoxyphenyl)-
acetic acid, DMF, room temp, 1 h; (b) acetic acid, 140 °C, 1 h; (c)
H2, 10% Pd/C, ethanol, room temp, 30 min; (d) 48% HBr/H2O, 100
°C, 15 h.
Sch em e 2a
a
Reagents and conditions: (a) RSO2Cl, pyridine, reflux, 18 h;
(b) H2, 10% Pd/C, ethanol/ethyl acetate, room temp, 15 h; (c) EDC,
HOBt, (4-phenoxyphenyl)acetic acid, DMF, room temp, 1 h; (d)
acetic acid, 140 °C, 1 h.
(4-phenoxyphenyl)acetic acid and o-phenylenediamine
(8), was the only significantly active compound (Ki < 2
µM) observed. With this structurally novel lead in hand,
we undertook an effort to explore benzimidazole sub-
stituent effects.
Ch em istr y
Compounds 7a -e were prepared from the appropri-
ately substituted phenylenediamines (8-12), which
were coupled to (4-phenoxyphenyl)acetic acid using a
standard amide coupling reaction,17 followed by dehy-
dration to the benzimidazole in acetic acid at reflux.18
Reduction of the nitro group of 7b gave 7g, and
hydrolysis of methyl ether 7c gave 7f.
A related series of sulfonamides (17a -e) were pre-
pared via the routes outlined in Scheme 2. The required
phenylenediamines (14-16) could be prepared from
nitro aromatic 13 via selective sulfonylation followed by
reduction of the nitro group (path i).19 These compounds
then were used as above in preparation of benzimida-
zoles 17a , 17b, and 17d . Alternatively, benzimidazole
7g could be sulfonylated to give 17c and 17e (path ii).
The syntheses of the piperidine derivatives followed
the general procedure shown in Scheme 3. The ap-
propriate benzyl phosphonates20 were prepared from
benzyl chlorides 20-24 and subjected to the Horner-
Emmons reaction21 with 4-benzylpiperidone. The result-
We then examined the SAR on the pendent phenyl
ring. As shown in Table 3, installation of a 2-fluoro
group on the phenyl ring gave 37a , a compound with a
0.85 nM Ki for NR2B. This modification further im-
proved the selectivity over hERG binding and R-adren-
ergic activity to >3000-fold and >800-fold, respectively.
To evaluate NR2 subtype selectivity more fully, com-

NMDA Antagonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 8 2091
Sch em e 3a
a
Reagents and conditions: (a) triethyl phosphite, 150 °C, 15 h; (b) sodium hydride, N-benzyl-4-piperidone, 1,3-dimethyl-2-imidazoline,
room temp, 20 min; (c) H2, 50 psi, Pd(OH)2/C, ethanol, room temp, 15 h; (d) ethyl bromoacetate, diisopropylethylamine, DMF, room temp,
1 h; (e) 6 N HCl; 100 °C, 1 h; (f) EDC, HOAt, triethylamine, phenylenediamine (8, 10, 14, 16), DMF, room temp, 20 min; (g) acetic acid,
140 °C, 15 min; (h) 48% HBr/H2O, 100 °C, 3 h.
Ta ble 1. In Vitro Binding Data for Phenoxyphenyl Benzimidazolesa
NR2B binding
NR2B Ca2+ influx
IC50 (nM)c
hERG
R1-adrenergic
compd
R1
R2
Ki (nM)b
IP (nM)d
IC50 (nM)e
7a
7b
7c
7d
7e
7f
7g
17a
17b
17c
17d
17e
18
H
H
260 */1.4
5400 */1.6
8400 */1.1
790 */1.5
140 */1.2
3.2 */1.3
180 */1.2
0.68 */1.4
3.0 */1.1
21 */1.5
200 */1.2
6600 */2.1
9200 */1.7
800 */1.4
150 */1.5
9.2 */1.7
78 */1.3
0.72 */1.2
2.1 */1.5
19 */1.4
2000 */1.8
770 */1.7
590 */2.0
1100 */2.4
860 */2.6
720 */1.6
120 */1.2
120 */1.1
1600 */1.1
400 */1.3
1900 */1.2
680 */1.1
2600 */1.7
640 */2.1
4200 */1.3
1200 */1.4
530 */1.3
3400 */1.0
5500 */1.1
200 */1.0
2600 */1.3
4000 */1.2
2800 */1.4
4800 */1.5
3100 */1.5
14000 */2.0
20000 */1.6
2000 */1.2
NO2
OMe
CN
H
OH
NH2
NHSO2Me
NHSO2Et
NHSO2Pr
H
H
H
OH
H
H
H
H
H
H
H
H
H
i
NHSO2 Pr
NHSO2Ph
NHAc
15 */1.1
17 */1.3
93 */1.2
470 */1.4
14 */1.1
49 */1.4
42 */2.8
25 */3.0
19
N(Me)SO2Me
a
All values are the geometric mean of at least n ) 4 measurements. The value shown in the table after the “*/” symbol is twice the
standard error of the geometric mean [2(SEGM)]. The confidence limits (95%) can be calculated by multiplying (/) and dividing (/) the
geometric mean by this value. For example, in the NR2B binding assay, compound 7a has a mean Ki of 260 nM with a 95% confidence
limit range of 186-364 nM. Inhibition of 3H-[(E)-N1-(2-methoxybenzyl)cinnamamidine] binding to hNR1a/NR2B receptors expressed in
b
Ltk- cells.22 c Fluorescent measurement of inhibition of Glu/Gly stimulated Ca2+ flux in Ltk- cells expressing the hNR1a/NR2B receptor.22
d
Inhibition of MK-499 binding to hERG in HEK293 cells.23 e Inhibition of R1-receptor binding on membranes prepared from rat brain.24
pound 37a was tested against the four known NR2B
subtypes in a whole-cell patch-clamp assay and was
shown to be selective for NR2B (Figure 3).
suggesting that the lack of pharmacologic activity was
due to poor brain penetration.
The benzylpiperidines (6c and 37a ) showed poor oral
bioavailability in rat but, in contrast, demonstrated good
pharmacokinetic profiles in dog, with low clearance and
iv half-lives in the 6-7 h range. On the basis of the
pharmacokinetic properties in dogs, we were interested
in evaluating compounds 6c and 37a in the rat carra-
geenan-induced mechanical hyperalgesia assay, with an
iv dosing protocol to overcome the poor plasma levels
generated after oral dosing in rats. Both compounds
showed good activity with compound 37a having an
ED50 of <3 mg/kg iv.
Compounds from each series described above were
evaluated in the carrageenan-induced mechanical hy-
peralgesia assay in rats7 and for pharmacokinetic
properties (Table 4).25 Methanesulfonamidobenzimida-
zole 17a had excellent oral bioavailabilty in rats;
however, it lacked any activity in the carrageenan-
induced mechanical hyperalgesia in rats at the highest
oral dose tested (30 mg/kg). Plasma and brain concen-
trations were measured following this experiment, and
these data showed a brain-to-plasma ratio of 0.038, thus

2092 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 8
McCauley et al.
Ta ble 2. In Vitro Binding Data for Benzylpiperidine Benzimidazolesa
NR2B binding
NR2B Ca2+ influx
hERG
R1-adrenergic
compd
R1
Ki (nM)b
IC50 (nM)c
IP (nM)d
IC50 (nM)e
6a
6c
6e
6f
H
OH
NHSO2Me
NHSO2 Pr
420 */1.1
1.5 */1.1
0.99 */1.5
240 */1.1
710 */1.3
8.2 */1.2
1.9 */1.3
300 */1.2
1400 */1.2
2600 */1.3
340 */1.7
2800 */1.2
670 */1.1
1500 */1.2
570 */1.1
i
3300 */1.1
a
All values are the geometric mean of at least n ) 4 measurements. The value shown in the table after the “*/” symbol is twice the
standard error of the geometric mean [2(SEGM)]. The confidence limits (95%) can be calculated by multiplying (/) and dividing (/) the
geometric mean by this value. For example, in the NR2B binding assay, compound 6a has a mean Ki of 420 nM with a 95% confidence
limit range of 382-462 nM. Inhibition of 3H-[(E)-N1-(2-methoxybenzyl)cinnamamidine] binding to hNR1a/NR2B receptors expressed in
b
Ltk- cells.22 c Fluorescent measurement of inhibition of Glu/Gly stimulated Ca2+ flux in Ltk- cells expressing the hNR1a/NR2B receptor.22
Inhibition of MK-499 binding to hERG in HEK293 cells.23 e Inhibition of R1-receptor binding on membranes prepared from rat brain.24
d
Ta ble 3. In Vitro Binding Data for Benzylpiperidine Benzimidazolesa
NR2B binding
NR2B Ca2+ influx
IC50 (nM)c
hERG
R1-adrenergic
compd
R
Ki (nM)b
IP (nM)d
IC50 (nM)e
37a
37b
37c
37d
37e
2-F
3-F
4-F
2,6-diF
4-Me
0.85 */1.1
4.2 */1.3
1.1 */1.1
0.82 */1.3
0.4 */1.8
9.7 */1.5
44 */1.3
12 */1.4
21 */1.3
5.7 */1.8
2900 */1.3
2100 */1.3
500 */1.4
3000 */1.3
390 */1.5
730 */1.1
520 */2.0
620 */1.4
2600 */1.2
830 */1.0
a
All values are the geometric mean of at least n ) 4 measurements. The value shown in the table after the “*/” symbol is twice the
standard error of the geometric mean [2(SEGM)]. The confidence limits (95%) can be calculated by multiplying (/) and dividing (/) the
geometric mean by this value. For example, in the NR2B binding assay, compound 37a has a mean Ki of 0.85 nM with a 95% confidence
limit range of 0.77-0.94 nM. Inhibition of 3H-[(E)-N1-(2-methoxybenzyl)cinnamamidine] binding to hNR1a/NR2B receptors expressed
b
in Ltk- cells.22 c Fluorescent measurement of inhibition of Glu/Gly stimulated Ca2+ flux in Ltk- cells expressing the hNR1a/NR2B
receptor.22 Inhibition of MK-499 binding to hERG in HEK293 cells.23 e Inhibition of R1-receptor binding on membranes prepared from
d
rat brain.24
peralgesia model and possesses excellent pharmacoki-
netic properties in dogs.
Exp er im en ta l Section
Gen er a l. All reagents and solvents were of commercial
quality and used without further purification unless indicated
otherwise. All reactions were carried out under an inert
1
atmosphere of nitrogen. H NMR spectra were obtained on a
Varian VXR-300S spectrometer or a Varian Unity Inova 400
spectrometer. Chemical shifts are reported in parts per million
relative to TMS as internal standard. Samples provided for
accurate mass measurement were taken up in acetonitrile/
water/glacial acetic acid (50:50:0.1% v/v). The solutions were
analyzed by use of electrospray ionization (ESI) or atmospheric
pressure chemical ionization (APCI) on either
a Bruker
Daltonics 3T or 7T Fourier transform ion cyclotron resonance
(FTICR) mass spectrometer. External calibration was ac-
complished with polypropylene glycol (425 or 750). Melting
points were determined in open glass capillaries using a
Thomas-Hoover UniMelt melting point apparatus and are
uncorrected. Elemental analyses were performed by Quantita-
tive Technologies Inc., Whitehouse, NJ . Silica gel chromatog-
raphy was carried out with an ISCO CombiFlash Sg 100c
purification system using ISCO silica gel RediSep cartridges.
Preparative reverse-phase HPLC was performed using a
Gilson 215 liquid handler and a YMC CombiPrep Pro C18
column (50 mm × 20 mm i.d.) with a linear gradient over 15
min (95:5 to 5:95 H2O/acetonitrile, containing 0.1% trifluoro-
acetic acid).
F igu r e 3. Inhibition of NMDA receptor activated currents
at recombinant human NMDA receptor subtypes. NR1a +
NR2A, NR2B, and NR2D were stably expressed in L(tk-) cells,
while NR1a + NR2C were expressed transiently in HEK
cells.26 Data represent the inhibition of maximally evoked
currents in response to a glutamate/glycine application and
are the mean ( SEM from at least five individual cells. Mean
data from NR1 + NR2B were fitted using the Hill equation.
In conclusion, we have developed two novel classes
of NR2B-selective NMDA receptor antagonists. The
piperidine class demonstrates efficacy in a rodent hy-

NMDA Antagonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 8 2093
Ta ble 4. In Vivo Evaluation of Selected Compounds
pharmacokinetic
pharmacokinetic
profile in dogsf
profile in ratse
carrageenan-induced
mechanical hyperalgesia
T1/2
(min)
Cl
T1/2
(min)
Cl
compd
in ratsa (mg/kg)
% F
((mL/min)/kg)
% F
((mL/min)/kg)
17a
6c
37a
>30, pob
97
20
6.4
118
>480
60
8.3
22.8
12.3
3.3 ( 0.3, ivc
<3, ivd
90
87
402
390
0.6
0.6
a
Carrageenan-induced mechanical hyperalgesia is defined as the difference in vocalization threshold between vehicle-treated rats
receiving ipl injections of carrageenan vs saline. Paw pressure scores for test-agent-treated rats are expressed as a percentage of the
hyperalgesia response induced by carrageenan. The ED50 value for test agents is defined as the dose of drug at which the paw pressure
b
score is 50% of the hyperalgesia response induced by carrageenan. Compound 17a showed no reduction in paw pressure score at the
d
highest oral dose tested (30 mg/kg); one determination. c Three ED50 determinations. Study doses ) 1, 3, and 10 mg/kg iv. One ED50
determination. Study doses ) 3 and 10 mg/kg iv. e Sprague-Dawley rats (n ) 3-4). Oral dose ) 10 mg/kg. Intravenous dose ) 2 mg/kg.
Interanimal variability was less than 20% for all values. Abbreviations: % F, oral bioavailability; Cl, clearance. f Mongrel dogs (n ) 2).
Oral dose ) 3 mg/kg. Intravenous dose ) 1 mg/kg. Interanimal variability was less than 20% for all values. Abbreviations: % F, oral
bioavailability; Cl, clearance.
Ca r r a geen a n -In d u ced Mech a n ica l H yp er a lgesia in
Ra ts. The ability of the agents to reverse carrageenan-induced
hyperalgesia was determined using the method described by
Boyce et al.7 In brief, mechanical paw pressure thresholds were
determined in male Sprague-Dawley rats (100-120 g) using
a modified Ugo Basile algesiometer by positioning the animal’s
hind paw over a convex surface (radius 2.5 mm) and gradually
increasing pressure applied to the dorsal surface until the
animals vocalized. Following a 1 h equilibration in the lab,
mechanical thresholds were determined for both hind paws
to provide a baseline for subsequent comparison following
injection of carrageenan into one paw. Rats then received an
intraplantar (ipl) injection of either carrageenan (Sigma; 4.5
mg in 0.15 mL of saline) or saline (0.15 mL) into one hind paw.
Post-treatment mechanical paw pressure thresholds of both
hind paws were determined 3 h after the ipl injections of
carrageenan or saline, with validation studies having estab-
lished 3 h as the peak time for development of carrageenan-
induced inflammation. Carrageenan-induced hyperalgesia was
defined as the difference in vocalization threshold between
vehicle-treated rats receiving ipl injections of carrageenan vs
saline. Paw pressure scores for test-agent-treated rats were
expressed as a percentage inhibition of the hyperalgesia
induced by carrageenan. Test agents were administered orally
by gavage in a vehicle of 1% methylcellulose aqueous suspen-
sion (n ) 8/dose) at 1 h prior to post-treatment paw pressure
thresholds determinations or intravenously in a vehicle of 50%
PEG-200/D5W (n ) 6/dose) at 15 min prior to post-treatment
paw pressure thresholds determinations.
Deter m in a tion of P la sm a a n d Br a in Con cen tr a tion s.
In some carrageenan-induced mechanical hyperalgesia studies,
after the determination of post-treatment mechanical paw
pressure thresholds, blood and brain samples were obtained
for the determination of test agent tissue concentration. A 1
mL blood sample was removed by cardiac puncture (25 gauge
needle containing 0.1 mL 3.8% citrate attached to a 3 mL
syringe) and spun to obtain plasma, which was frozen (-70
°C). The animals were then euthanized in a carbon dioxide
chamber, and the forebrain was removed rapidly and frozen.
Mobile phase A was water/methanol (90:10) with 0.1%
formic acid. Mobile phase B was 100% acetonitrile. Plasma
samples were prepared using a semiautomated protein pre-
cipitation method assisted by a robotic sample processor (Tecan
Genesis RSP 150, Tecan, Durham, NC) by mixing 100 µL of
plasma, 50 µL of the internal standard solution (10 000 ng/
mL in mobile phase A), and 400 µL of acetonitrile in a 96-well
plate. The 96-well plate was capped, vortex, and centrifuged
at 3740g for 15 min. After centrifugation, a 450 µL aliquot of
the supernatant was removed, transferred into a second 96-
well plate, and evaporated. Samples were reconstituted in 200
µL of mobile phase A using the Tomtec Quadra 96 (Tomtec,
Hamden, CT) and transferred into glass inserts for analysis.
Brain samples were weighed exactly, placed into a 20 mL
plastic scintillation, and homogenized in mobile phase A (1/5,
w/v), yielding a solution of 0.166 g of brain tissue per mL of
brain homogenate. Brain samples were prepared by pipetting
1 mL of brain homogenate into a microcentrifuge tube and
centrifuging at 13500g for 15 min. After centrifugation, the
microcentrifuge tubes were transferred to the Tecan Genesis
RSP for additional liquid transfers, in which 200 µL of brain
homogenate supernatant was mixed with 50 µL of the internal
standard solution and 700 µL of acetonitrile in a 96-well plate.
The 96-well plate was capped, vortex, and centrifuged at 3740g
for 15 min. After centrifugation, a 450 µL aliquot of the
supernatant was removed, transferred into a second 96-well
plate, and evaporated. Samples were reconstituted in 200 µL
of mobile phase A using the Tomtec Quadra 96 and transferred
into glass inserts for analysis.
Samples were separated chromatographically using an
Agilent 1100 series HPLC instrument (Agilent Technologies,
Palo Alto, CA) and a CTC PAL autosampler (LEAP Technolo-
gies, Carboro, NC). A Prodigy 5 1 ODS3 (50 mm × 2 mm)
analytical column (Phenomenex, Torrance, CA) was used for
the analysis. Samples were analyzed on a PE/Sciex API 2000
triple quadrupole mass spectrometer (PE Sciex, Toronto,
Canada).
P h a r m a cok in etics. Pharmacokinetic characterization of
test agents was conducted in conscious male Sprague-Dawley
rats (300-500 g; n ) 3-4/study) or male and female beagle
dogs (13-15 kg; n ) 2/study). In both species, single doses of
test agents were administered either intravenously in a vehicle
of 100% DMSO or orally by gavage in a vehicle of 1%
methylcellulose aqueous suspension. Typical test doses were
2 mg/kg iv and 10 mg/kg po to rats and 1 mg/kg iv and 1-3
mg/kg po to dogs. Blood samples for the determination of test
agent plasma concentration were obtained at multiple time
points up to 24 h after single-dose test-agent administration.
In h ibition of NMDA Recep tor -Activa ted Cu r r en ts a t
Recom bin a n t Hu m a n NMDA Recep tor Su btyp es. Whole-
cell patch-clamp experiments were performed using an Axo-
clamp 200B on coverslip-plated L(tk-) cells stably transfected
with NR1a/NR2A, NR1a/NR2B, or NR1a/NR2D receptors, and
HEK cells were transiently transfected with NR1a/NR2C
receptors. The external recording solution consisted of the
following (in mM): NaCl (149), KCl (3.25), CaCl2 (2), HEPES
(10), glucose (11), sucrose (21.9); pH 7.4. This buffer solution
was superfused at a rate of 0.7-2.0 mL/min. The recording
pipet solution was composed of the following (in mM): CsF
(120), CsCl (10), EGTA (10), CaCl2 (0.5); pH 7.25. Agonists and
antagonist were applied locally by fast perfusion from a double-
barreled pipet, and experiments were performed at room
temperature. Inhibition curves for NMDA antagonists were
obtained in the presence of 10 µM glutamate and 1 µM glycine
(10 µM for NR1a/NR2A). Increasing concentrations of antago-
nist were preapplied for 30 s followed by two coapplications of
Glu/Gly for 5 s. Inhibition of the second Glu/Gly response in
the presence of antagonist was determined.
2-(4-P h en oxyben zyl)ben zim id a zole (7a ). To a solution
of (4-phenoxyphenyl)acetic acid (250 mg, 1.10 mmol) in di-
methylformamide (5 mL) was added 1-ethyl-3-(3-dimethylami-
nopropyl)carbodiimide hydrochloride (EDC) (252 mg, 1.31
mmol), 1-hydroxybenzotriazole hydrate (HOBt) (178 mg, 1.31

2094 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 8
McCauley et al.
mmol), and phenylenediamine 8 (124 mg, 1.15 mmol). The
reaction mixture was stirred at room temperature for 1 h
followed by quenching with aqueous NaHCO3 and ethyl
acetate. The layers were separated, and the organic layer was
washed twice with water, dried over Na2SO4, filtered, and
concentrated.
(d, 2 H), 6.63 (s, 1 H), 6.57 (d, 1 H), 4.19 (s, 2 H) ppm; HRMS
(ESI) m/z 316.1444 [(M + H)+, calcd for C20H18N3O, 316.1445].
Anal. (C20H17N3O‚0.4H2O) C, H, N.
N-[2-(4-P h en oxyb en zyl)b en zim id a zol-5-yl]m et h a n e-
su lfon a m id e (17a ). Using the above procedure for 7a with
N-(3,4-diaminophenyl)methanesulfonamide (14) followed by
silica gel chromatography (gradient elution, dichloromethane
to 90:10:1 dichloromethane/methanol/NH4OH) provided 17a .
The HCl salt was then prepared via treatment with HCl/ether
and concentration in vacuo. Recrystallization from 2-propanol
gave the HCl salt of 17a as a white crystalline solid: mp )
221-222 °C; 1H NMR (300 MHz, CD3OD) δ 7.71 (m, 2 H), 7.39
(m, 5 H), 7.16 (t, 1 H), 7.01 (m, 4 H), 4.53 (s, 2 H), 2.98 (s, 3 H)
ppm; HRMS (ESI) m/z 394.1231 [(M + H)+, calcd for
The crude product was dissolved in acetic acid (10 mL) and
heated to 140 °C for 1 h. The reaction mixture was cooled,
concentrated, and partitioned between aqueous 1 M NaOH and
ethyl acetate, and the organic layer was dried over Na2SO4,
filtered, and concentrated. The crude oil was purified by silica
gel chromatography (gradient elution, 1:1 hexanes/ethyl ac-
etate to ethyl acetate) to give 7a (240 mg, 73% yield) as a white
amorphous solid: 1H NMR (400 MHz, CD3OD) δ 7.55-7.40
(m, 2 H), 7.33 (m, 4 H), 7.19 (dd, 2 H), 7.07 (t, 1 H), 6.92 (m,
4 H), 4.21 (s, 2 H) ppm; HRMS (ESI) m/z 301.1327 [(M + H)+,
calcd for C20H17N2O, 301.1335]. Anal. (C20H16N2O) C, H, N.
5-Nitr o-2-(4-p h en oxyben zyl)ben zim id a zole (7b). Using
the above procedure for 7a with 4-nitro-1,2-phenylenediamine
(9) followed by silica gel chromatography (gradient elution,
10:1 hexanes/ethyl acetate to ethyl acetate) provided 7b as a
yellow amorphous solid: 1H NMR (400 MHz, CDCl3) δ 9.33
(d, 1 H), 8.20 (d, 1 H), 7.39 (t, 2 H), 7.31 (m, 3 H), 7.12 (t, 1 H),
7.04 (m, 4 H), 4.34 (s, 2 H) ppm; HRMS (ESI) m/z 346.1183
[(M + H)+, calcd for C20H16N3O3, 346.1186]. Anal. (C20H15N3O3‚
1.1H2O) C, H, N.
5-Meth oxy-2-(4-ph en oxyben zyl)ben zim idazole (7c). Us-
ing the above procedure for 7a with 4-methoxy-1,2-phenylene-
diamine (10) followed by silica gel chromatography (gradient
elution, 10:1 hexanes/ethyl acetate to ethyl acetate) provided
7c as a white amorphous solid: 1H NMR (300 MHz, CD3OD)
δ 7.60 (d, 1 H), 7.39 m, 4 H), 7.17 (m, 3 H), 7.00 (m, 4 H), 4.49
(s, 2 H), 3.89 (s, 3 H) ppm; HRMS (ESI) m/z 331.1437 [(M +
H)+, calcd for C21H19N2O2, 331.1441]. Anal. (C21H18N2O2‚
0.1H2O) C, H, N.
2-(4-P h en oxyben zyl)ben zim idazole-5-car bon itr ile (7d).
Using the above procedure for 7a with 3,4-diaminobenzonitrile
(11) followed by silica gel chromatography (gradient elution,
9:1 hexanes/ethyl acetate to ethyl acetate) provided 7d as a
white amorphous solid: 1H NMR (300 MHz, DMSO-d6) δ 8.04
(s, 1 H), 7.62 (d, 2 H), 7.58 (d, 2 H), 7.37 (m, 4 H), 7.11 (t, 1 H),
6.96 (m, 4 H), 4.11 (s, 2 H) ppm; HRMS (ESI) m/z 326.1288
[(M + H)+, calcd for C21H16N3O, 326.1288]. Anal. (C21H15N3O‚
0.1H2O) C, H, N.
2-(4-P h en oxyben zyl)ben zim id a zol-4-ol (7e). Using the
above procedure for 7a with 2,3-diaminophenol (12) followed
by silica gel chromatography (gradient elution, 10:1 hexanes/
ethyl acetate to ethyl acetate) provided 7e as a white amor-
phous solid: 1H NMR (400 MHz, CDCl3) δ 7.34 (t, 2 H), 7.28
(m, 2 H), 7.12 (t, 2 H), 7.00 (m, 4 H), 6.88 (d, 1 H), 6.79 (d, 1
H), 4.31 (s, 2 H), 2.18 (s, 1 H) ppm; HRMS (ESI) m/z 317.1284
[(M + H)+, calcd for C20H17N2O2, 317.1285]. Anal. (C20H16N2O2‚
0.7MeOH) C, H, N.
C
21H20N3O3S, 394.1220]. Anal. (C21H19N3O3S‚HCl) C, H, N.
N-[2-(4-P h en oxyben zyl)ben zim id a zol-5-yl]eth a n esu l-
fon a m id e (17b). Using the above procedure for 7a with
N-(3,4-diaminophenyl)ethanesulfonamide (15) followed by silica
gel chromatography (gradient elution, dichloromethane to 90:
10:1 dichloromethane/methanol/NH4OH) provided 17b . The
HCl salt was then prepared via treatment with HCl/ether and
concentration in vacuo. Recrystallization from 2-propanol gave
the HCl salt of 17b as a white crystalline solid: mp ) 193-
195 °C; 1H NMR (400 MHz, CD3OD) δ 7.68 (m, 2 H), 7.38 (m,
5 H), 7.13 (t, 1 H), 7.01 (m, 4 H), 4.50 (s, 2 H), 3.12 (q, 2 H),
1.30 (t, 3 H) ppm; HRMS (ESI) m/z 408.1382 [(M + H)+, calcd
for C22H22N3O3S, 408.1377]. Anal. (C22H21N3O3S‚HCl) C, H, N.
N-[2-(4-P h en oxyben zyl)ben zim id a zol-5-yl]p r op a n e-1-
su lfon a m id e (17c). To a solution of 7g (300 mg, 0.95 mmol)
in pyridine (5 mL) was added n-propylsufonyl chloride (136
mg, 0.95 mmol). The reaction mixture was heated and stirred
at reflux for 18 h. Water was then added, and the mixture
was extracted with dichloromethane. The organic layer was
dried over Na2SO4, filtered, concentrated, and purified by
reverse-phase HPLC to give the trifluoroacetate salt of 17c
as a white amorphous solid: 1H NMR (400 MHz, CD3OD) δ
7.81 (d, 2 H), 7.40-7.35 (m, 5 H), 7.16 (t, 1 H), 7.05 (m, 4 H),
4.52 (s, 2 H), 3.08 (dd, 2 H), 1.79 (m, 2 H), 0.98 (t, 3 H) ppm;
HRMS (ESI) m/z 422.1526 [(M + H)+, calcd for C23H24N3O3S,
422.1533]. Anal. (C23H23N3O3S‚TFA) C, H, N.
N-[2-(4-P h en oxyben zyl)ben zim id a zol-5-yl]p r op a n e-2-
su lfon a m id e (17d ). Using the above procedure for 7a with
N-(3,4-diaminophenyl)propane-2-sulfonamide (16) followed by
silica gel chromatography (gradient elution, dichloromethane
to 90:10:1 dichloromethane/methanol/NH4OH) provided 17d .
The HCl salt was then prepared via treatment with HCl/ether
and concentration in vacuo. Recrystallization from 2-propanol
gave the HCl salt of 17d as a white crystalline solid: mp )
206-207 °C; 1H NMR (400 MHz, CD3OD) δ 7.62 (m, 2 H), 7.35
(m, 5 H), 7.10 (t, 1 H), 6.97 (m, 4 H), 4.46 (s, 2 H), 3.25 (m, 1
H), 1.30 (d, 6 H) ppm; HRMS (ESI) m/z 422.1538 [(M + H)+,
calcd for C23H24N3O3S, 422.1533]. Anal. (C23H23N3O3S‚HCl) C,
H, N.
2-(4-P h en oxyben zyl)ben zim id a zol-5-ol (7f). A solution
of 7c (100 mg, 0.30 mmol) in HBr/H2O (48%, 2 mL) was heated
to 100 °C for 15 h. The reaction mixture was cooled, concen-
trated, and purified by preparative reverse-phase HPLC to give
the trifluoroacetate salt of 7f. The free base was prepared by
dissolving the residue in ethyl acetate, washing with saturated
aqueous NaHCO3, drying the organic over Na2SO4, filtering,
and concentrating to give 7f as a white amorphous solid (85
mg, 90% yield): 1H NMR (300 MHz, DMSO-d6) δ 8.99 (s, 1
H), 7.38 (m, 5 H), 7.22 (d, 1 H), 7.09 (t, 1 H), 6.95 (m, 3 H),
6.77 (s, 1 H), 6.59 (dd, 1 H), 4.05 (s, 2 H) ppm; HRMS (ESI)
m/z 317.1285 [(M + H)+, calcd for C20H17N2O2, 317.1291]. Anal.
(C20H16N2O2) C, H, N.
2-(4-P h en oxyben zyl)ben zim id a zol-5-a m in e (7g). To a
solution of 7b (1.09 g, 3.16 mmol) in ethanol (15 mL) was added
10% Pd/C (200 mg). The mixture was stirred at room temper-
ature under a balloon of hydrogen gas for 30 min. The reaction
mixture was filtered through Celite, and the catalyst washed
with ethanol. The filtrate was concentrated to give 7g as a
yellow amorphous solid (965 mg, 97% yield): 1H NMR (300
MHz, CDCl3) δ 7.21 (m, 6 H), 7.03 (t, 1 H), 6.87 (d, 2 H), 6.73
N-[2-(4-P h en oxyben zyl)ben zim id a zol-5-yl]ben zen esu l-
fon a m id e (17e). Using the above procedure for 17c with
phenylsulfonyl chloride followed by silica gel chromatography
(gradient elution, 2:1 hexanes/ethyl acetate to 95:5:0.5 ethyl
acetate/methanol/NH4OH) provided 17e as a white amorphous
solid: 1H NMR (400 MHz, CDCl3) δ 8.90 (s, 1 H), 7.72 (d, 2
H), 7.51 (t, 1 H), 7.29-7.43 (m, 5 H), 7.28 (s, 1 H), 7.13 (t, 1
H), 7.05 (d, 2 H), 6.98 (d, 2 H), 6.66 (br s, 1 H), 6.55 (br s, 1 H),
4.22 (s, 2 H) ppm; HRMS (ESI) m/z 456.1359 [(M + H)+, calcd
for C26H22N3O3S, 456.1298]. Anal. (C26H21N3O3S‚0.5MeOH) C,
H, N.
N-[2-(4-P h en oxyb en zyl)b en zim id a zol-5-yl]a cet a m id e
(18). Using the above procedure for 17c with acetic anhydride
followed by silica gel chromatography (gradient elution, dichlo-
romethane to 85:15:1.5 dichloromethane/methanol/NH4OH)
provided 18 as a clear oil: 1H NMR (400 MHz, CDCl3) δ 7.95
(br s, 1 H), 7.51 (br s, 1 H), 7.34 (m, 3 H), 7.24 (m, 2 H), 7.11
(t, 2 H), 6.98 (m, 5 H), 4.27 (s, 3 H), 3.50 (s, 2 H) ppm; HRMS
(ESI) m/z 358.1550 [(M + H)+, calcd for C22H20N3O2, 358.1545].
Anal. (C22H19N3O2‚0.75H2O) C, H, N.

NMDA Antagonists
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 8 2095
N-Met h yl-N-[2-(4-p h en oxyb en zyl)b en zim id a zol-5-yl]-
m eth a n esu lfon a m id e (19). To a solution of 17a (15 mg, 0.04
mmol) in dimethylformamide (1 mL) was added cesium
carbonate (25 mg, 0.08 mmol) and methyl iodide (3 µL, 0.04
mmol). The reaction mixture was stirred at room temperature
for 2 h followed by quenching with aqueous NaHCO3 and ethyl
acetate. The layers were separated, and the organic was
washed twice with water, dried over Na2SO4, filtered, and
concentrated. Purification by silica gel chromatography (gradi-
ent elution, dichloromethane to 98:2:0.2 dichloromethane/
methanol/NH4OH) gave 19 as a clear oil (8.1 mg, 52% yield):
1H NMR (400 MHz, CDCl3) δ 7.55 (m, 2 H), 7.35 (d, 1 H), 7.32
(d, 1 H), 7.24 (m, 2 H), 7.11 (t, 1 H), 6.99 (m, 5 H), 4.25
(s, 2 H), 3.35 (s, 3 H), 2.86 (s, 3 H) ppm; HRMS (ESI) m/z
408.1377 [(M + H)+, calcd for C22H22N3O3S, 408.1374]. Anal.
(C22H21N3O3S‚0.8MeOH) C, H, N.
4-(2-F lu or oben zyl)p ip er id in e (26). A neat mixture of
2-fluorobenzyl chloride (20) (10.0 g, 69.0 mmol) and triethyl
phosphite (11.5 g, 69.0 mmol) was heated to 150 °C and stirred
for 15 h. The reaction mixture was concentrated twice from
toluene and then concentrated and purified by silica gel
chromatography (gradient elution, 1:1 hexanes/ethyl acetate
to 10% methanol/ethyl acetate) to give diethyl 2-fluoroben-
zylphosphonate.
To a solution of diethyl 2-fluorobenzylphosphonate (16 g,
69 mmol) in 1,3-dimethyl-2-imidazolidinone (25 mL) was added
sodium hydride (4.4 g, 110 mmol) followed by slow addition of
a solution of N-benzyl-4-piperdinone (13 g, 69 mmol). The
reaction mixture was stirred for 20 min, cooled to 0 °C, and
carefully quenched with water. Dichloromethane was added,
and the layers were separated. The organic layer was dried
over Na2SO4, filtered, and concentrated to give 1-benzyl-4-(2-
fluorobenzyl)piperidine, which was used without further pu-
rification.
To a solution of 1-benzyl-4-(2-fluorobenzyl)piperidine (7 g,
25 mmol) in ethanol (150 mL) was added 10% palladium
hydroxide (500 mg). The reaction mixture was placed on a Parr
shaker with 50 psi of hydrogen and shaken for 15 h. The
reaction mixture was filtered through Celite, concentrated, and
purified by silica gel chromatography (gradient elution, 95:5:
0.5 to 90:10:1 dichloromethane/methanol/NH4OH) to give 4-(2-
fluorobenzyl)piperidine (26): mass spectrum m/z 321 [(M +
H)+, calcd for C20H24N4, 321].
(4-Ben zylp ip er id in -1-yl)a cetic Acid (31). To a solution
of 4-benzylpiperidine (25) (1.0 g, 5.7 mmol) in dimethylforma-
mide (20 mL) was added diisopropylethylamine (990 µL, 5.7
mmol) and ethyl bromoacetate (637 µL, 5.7 mmol), and the
reaction mixture was stirred at room temperature for 1 h. The
reaction mixture was partitioned between ethyl acetate and
aqueous NaHCO3, and the organic layer was dried over Na2-
SO4, filtered, and concentrated. The crude oil was purified by
silica gel chromatography (gradient elution, 4:1 hexanes/ethyl
acetate to ethyl acetate) to give ethyl (4-benzylpiperidin-1-yl)-
acetate.
Ethyl (4-benzylpiperidin-1-yl)acetate (700 mg, 2.6 mmol)
was dissolved in 6 N HCl (5 mL), and the mixture was heated
to 100 °C for 1 h. The reaction mixture was cooled and
concentrated to give the HCl salt of 31 as a white solid that
was used without further purification.
2-[(4-Ben zylp ip er id in -1-yl)m eth yl]-5-m eth oxyben zim i-
d a zole (6b). To a solution of (4-benzylpiperidin-1-yl)acetic acid
hydrochloride salt (31) (2.0 g, 7.41 mmol) in dimethylforma-
mide (20 mL) was added EDC (1.56 g, 8.16 mmol), 1-hydroxy-
7-azabenzotriazole (HOAt) (1.11 g, 8.16 mmol), 4-methoxy-1,2-
phenylenediamine (10) (1.02 g, 7.41 mmol), and triethylamine
(2.06 mL, 14.8 mmol). The reaction mixture was stirred at
room temperature for 20 min followed by quenching with
aqueous NaHCO3 and ethyl acetate. The layers were sepa-
rated, and the organic portion was washed twice with water,
dried over Na2SO4, filtered, and concentrated.
by silica gel chromatography (gradient elution, 95:5:0.5 to 80:
20:2 dichloromethane/methanol/NH4OH) to give methoxyben-
zimidazole 6b (1.86 g, 75% yield, two steps) as a white
amorphous solid: 1H NMR (300 MHz, CD3OD) δ 7.46 (d, 1 H),
7.28 (m, 2 H), 7.20 (t, 1 H), 7.13 (d, 2 H), 7.05 (br.s, 1 H), 6.87
(dd, 1 H), 3.87 (s, 2 H), 3.84 (s, 3 H), 2.94 (d, 2 H), 2.57 (d, 2
H), 2.23 (t, 2 H), 1.68 (d, 2 H), 1.59 (m, 1 H), 1.42 (q, 2 H)
ppm; HRMS (ESI) m/z 336.2070 [(M + H)+, calcd for C21H26N3O,
336.2058]. Anal. (C21H25N3O‚0.65H2O) C, H, N.
2-[(4-Ben zylp ip er id in -1-yl)m et h yl]b en zim id a zol-5-ol
(6c). Benzimidazole 6b (1.86 g, 5.55 mmol) was dissolved in
HBr/H2O (48%, 10 mL), and the mixture was heated to 100
°C for 3 h. The reaction mixture was cooled, concentrated, and
purified by silica gel chromatography (gradient elution, dichlo-
romethane to 80:20:2 dichloromethane/methanol/NH4OH). The
HCl salt was then prepared via treatment with HCl/ether and
concentration in vacuo. Trituration in methanol/ether (1:2)
gave the HCl salt of 6c as a white crystalline solid (1.0 g, 56%
1
yield): mp ) 235 °C dec; H NMR (400 MHz, CD3OD) δ 7.61
(d, 1 H), 7.24 (t, 2 H), 7.17 (m, 5 H), 4.75 (s, 2 H), 3.60 (d, 2 H),
3.15 (t, 2 H), 2.60 (d, 2 H), 1.91 (m, 3 H), 1.61 (m, 2 H) ppm;
HRMS (ESI) m/z 322.1914 [(M + H)+, calcd for C20H24N3O,
322.1914]. Anal. (C20H23N3O‚2HCl‚0.9iPrOH) C, H, N.
N-{2-[(4-Ben zylp ip er id in -1-yl)m eth yl]ben zim id a zol-5-
yl}m eth a n esu lfon a m id e (6d ). Using the above procedure for
6b with N-(3,4-diaminophenyl)methanesulfonamide (14) pro-
vided 6d . The HCl salt was then prepared via treatment with
HCl/ether and concentration in vacuo. Recrystallization from
4:1 methanol/ethyl acetate gave the HCl salt of 6d as a white
1
crystalline solid: mp ) 230 °C dec; H NMR (300 MHz, CD3-
OD) δ 7.79 (d, 1 H), 7.75 (s, 1 H), 7.42 (d, 1 H), 7.32-7.17 (m,
5 H), 4.85 (s, 2 H), 3.65 (d, 2 H), 3.20 (t, 2 H), 3.00 (s, 3 H),
2.62 (d, 2 H), 2.00-1.88 (m, 3 H), 1.67 (m, 2 H) ppm; HRMS
(ESI) m/z 399.1851 [(M + H)+, calcd for C21H27N4O2S, 399.1849].
Anal. (C21H26N4O2S‚2HCl) C, H, N.
N-{2-[(4-Ben zylp ip er id in -1-yl)m eth yl]ben zim id a zol-5-
yl}p r op a n e-2-su lfon a m id e (6e). Using the above procedure
for 6b with N-(3,4-diaminophenyl)propane-2-sulfonamide (16)
followed by purification by preparative reverse-phase HPLC
provided 6e as a white amorphous solid: 1H NMR (400 MHz,
CDCl3) δ 7.52 (s, 1 H), 7.47 (d, 1 H), 7.22 (m, 2 H), 7.11 (m, 4
H), 3.75 (s, 2 H), 3.20 (m, 1 H), 2.90 (m, 2 H), 2.51 (d, 2 H),
2.10 (t, 2 H), 1.61 (m, 2 H), 1.54 (m, 1 H), 1.36 (m, 2 H), 1.31
(d, 6 H) ppm; HRMS (ESI) m/z 427.2161 [(M + H)+, calcd for
C
23H31N4O2S, 427.2162]. Anal. (C23H30N4O2S‚0.3TFA) C, H, N.
2-{[4-(2-Flu or oben zyl)p ip er id in -1-yl]m eth yl}ben zim id -
a zol-5-ol (37a ). Using the above procedure for 6b with [4-(2-
fluorobenzyl)piperidinyl]acetic acid (32) followed by silica gel
chromatography (gradient elution, 95:5:0.5 to 80:20:2 dichlo-
romethane/methanol/NH4OH) provided 37a . The HCl salt was
then prepared via treatment with HCl/ether and concentration
in vacuo. Recrystallization from 2-propanol gave the HCl salt
of 37a as a white crystalline solid: mp ) 240 °C dec; 1H NMR
(400 MHz, CD3OD) δ 7.61 (d, 1 H), 7.23 (m, 2 H), 7.07 (m, 4
H), 4.65 (s, 2 H), 3.59 (d, 2 H), 3.10 (t, 2 H), 2.67 (d, 2 H), 1.93
(d, 3 H), 1.62 (m, 2 H) ppm; HRMS (ESI) m/z 340.1821 [(M +
H)+, calcd for C20H23FN3O, 340.1820]. Anal. (C20H22FN3O‚
2HCl) C, H, N.
2-{[4-(3-Flu or oben zyl)p ip er id in -1-yl]m eth yl}ben zim id -
a zol-5-ol (37b). Using the above procedure for 6b with [4-(3-
fluorobenzyl)piperidinyl]acetic acid (33) followed by silica gel
chromatography (gradient elution, 95:5:0.5 to 80:20:2 dichlo-
romethane/methanol/NH4OH) provided 37b. The HCl salt was
then prepared via treatment with HCl/ether and concentration
in vacuo. Recrystallization from 2-propanol gave the HCl salt
of 37b as a white crystalline solid: mp ) 215 °C dec; 1H NMR
(300 MHz, CD3OD) δ 7.70 (d, 1 H), 7.30 (m, 1 H), 7.17 (m, 2
H), 6.93 (m, 3 H), 4.90 (s, 2 H), 3.63 (d, 2 H), 3.22 (t, 2 H), 2.62
(d, 2 H), 1.92 (d, 3 H), 1.63 (m, 2 H) ppm; HRMS (ESI) m/z
340.1821 [(M + H)+, calcd for C20H23FN3O, 340.1820]. Anal.
(C20H22FN3O‚2HCl‚0.65iPrOH) C, H, N.
The crude oil was dissolved in acetic acid (20 mL) and heated
to 140 °C for 15 min. The reaction mixture was cooled,
concentrated twice from toluene, and used without further
purification. An aliquot of the reaction mixture was purified
2-{[4-(4-Flu or oben zyl)p ip er id in -1-yl]m eth yl}ben zim id -
a zol-5-ol (37c). Using the above procedure for 6b with [4-(4-
fluorobenzyl)piperidinyl]acetic acid (34) followed by silica gel

2096 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 8
McCauley et al.
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chromatography (90:10:1 dichloromethane/methanol/NH4OH)
provided 37c as a white amorphous solid: 1H NMR (400 MHz,
CDCl3) δ 7.40 (br s, 1 H), 7.28 (s, 1 H), 7.05 (m, 2 H), 6.92 (m,
2 H), 6.81 (d, 1 H), 3.75 (s, 2 H), 2.91 (d, 2 H), 2.47 (d, 2 H),
2.12 (t, 2 H), 1.58 (m, 2 H), 1.50 (m, 1 H), 1.28 (m, 2 H) ppm;
HRMS (ESI) m/z 340.1808 [(M + H)+, calcd for C20H23FN3O,
340.1820]. Anal. (C20H22FN3O‚0.4 dichloromethane) C, H, N.
2-{[4-(2,6-Diflu or oben zyl)p ip er id in -1-yl]m eth yl}ben z-
im id a zol-5-ol (37d ). Using the above procedure for 6b with
[4-(2,6-difluorobenzyl)piperidinyl]acetic acid (35) followed by
silica gel chromatography (gradient elution, 95:5:0.5 to 80:20:2
dichloromethane/methanol/NH4OH) provided 37d . The HCl
salt was then prepared via treatment with HCl/ether and
concentration in vacuo. Recrystallization from 2-propanol gave
the HCl salt of 37d as a white crystalline solid: mp ) 230 °C
1
dec; H NMR (300 MHz, CD3OD) δ 7.65 (d, 1 H), 7.29 (m, 1
H), 7.15 (m, 2 H), 6.95 (t, 2 H), 4.72 (s, 2 H), 3.61 (d, 2 H), 3.14
(t, 2 H), 2.72 (d, 2 H), 1.92 (d, 3 H), 1.70 (m, 2 H) ppm; HRMS
(ESI) m/z 358.1725 [(M + H)+, calcd for C20H22F2N3O, 358.1726].
Anal. (C20H21F2N3O‚3HCl‚0.6H2O) C, H, N.
2-{[4-(4-Meth ylben zyl)piper idin -1-yl]m eth yl}ben zim id-
a zol-5-ol (37e). Using the above procedure for 6b with [4-(4-
methylbenzyl)piperidinyl]acetic acid (36) followed by silica gel
chromatography (gradient elution, 90:10:1 to 80:20:2 dichlo-
romethane/methanol/NH4OH) provided 37e as a white amor-
phous solid: 1H NMR (400 MHz, CDCl3) δ 7.39 (br s, 1 H),
7.28 (s, 1 H), 7.10 (d, 2 H), 6.95 (d, 2 H), 6.81 (d, 1 H), 3.70 (s,
2 H), 2.90 (d, 2 H), 2.40 (d, 2 H), 2.29 (s, 3 H), 2.10 (t, 2 H),
1.57 (m, 2 H), 1.48 (m, 1 H), 1.23 (m, 2 H) ppm; HRMS (ESI)
m/z 336.2082 [(M + H)+, calcd for C21H26N3O, 336.2071]. Anal.
(C21H25N3O‚0.95H2O) C, H, N.
Ack n ow led gm en t. The authors thank Dr. Charles
W. Ross, III and Ms. J oan S. Murphy for determination
of high-resolution mass spectra.
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